Surgeons strive for accurate, replicable surgical techniques so that precise fits can be obtained between prothesis and bone. Increased contact area between bone and prosthesis has been shown to improve long-term fixation in cementless applications. Accurate bone preparation for cemented protheses will also provide improved fixation due to precise and optimal cement mantle thickness between bone and prosthesis. To accomplish "optimal" femoral envelope preparation, surgeons make use of instruments in a predetermined technique.
In the prior art, in performing total hip arthroplasty, preparation of the femoral envelope is traditionally divided into four steps, in general. In the first step, a starter awl (which is sometimes referred to as a "Charnley awl") is used to open the femur. In that step, a starter awl is used to define an opening in the proximal canal. Such starter awls are generally small diameter, straight-fluted reamers, which are manually introduced into the femoral canal to open a track into which subsequent progressive distal reamers may be introduced.
In the second step of the preparation of the femoral envelope, a short guide wire is passed into the femoral canal; and a set of four to five either rigid or flexible distal reamers with progressively larger sizes are passed into the canal until "circumferential cortical resonance" (which is also called "resistance to distal passage") is noted. The reamers should pass to the depth of the isthmus in the femoral canal (which is defined here as a constriction between the two larger parts of the femoral canal; that is, the isthmus is the narrow part of the femoral canal between the condyles and the proximal femur). In this second step, multiple iterations of distal reamers must be passed into the isthmus to size the passage up to the proper diameter.
In the third step of the traditional method in the prior art, the proximal portion of the femoral canal to the point of the isthmus is conically reamed. That is, the metaphyseal and diaphyseal regions are prepared using a multiplicity of proximal tapered midshaft reamers. These reamers have a non-cutting bullet tip that rides in the prepared isthmus distally. The tapered midshaft reamers remove proximal lateral bone and make the fourth step in the 4-step procedure easier.
The fourth step is to broach the metaphysis and diaphysis multiple times.
Thus, to summarize, the preparation sequence of the prior art is to use a starter awl, then distally ream the isthmus multiple times, then ream the proximal portion of the femoral canal (i.e., the metaphyseal and diaphyseal regions) multiple times, and then broach the metaphyseal and diaphyseal regions multiple times.
In the 4-step procedure, the last three steps must be completed multiple times, carefully using increasingly larger instruments in each iteration until final sizing to fit has been attained. These multiple iterations per step are time consuming, yet essential when performing hip surgery. Sizing up through multiple iterations minimizes the chances of damaging the femur by forcing too large an instrument into the bone.
It is an object of this invention to provide an apparatus and a kit of apparatuses for reducing the number of multiple iterations needed for preparation of the femoral canal.
A further object of this invention is to provide a method in which the number of iterations required in preparation of the femoral canal is significantly reduced.
Yet another object of this invention is a device and a kit of awls which can be used so as to both open the femoral canal and then size the distal portion of any human femoral canal using at most only two such awls and thereby obviating the use of the four to five distal reamers which in the past have been required generally in the second step of the 4-step procedure described above.
Yet another object of this invention is an awl which will be used both as a starter awl and will also size the femoral canal, with at most only two such awls being necessary for starting and sizing distally any human femoral canal, (i.e., performance of steps one and two described above, in which the femoral canal is opened and the isthmus is prepared).